I wanted to resurrect this before and didn't - BUT...
The mising ingredient seems to be the process for Sovereign's voice, which no one seems to have written down. I did, after some experimentation.
A good mic is a good idea, and a windscreen. Sibilance gets nasty with this processing (s-sounds).
Also what enwinor said above. Go for deep but don't strain, you get deep from the processing. Evenness matters more.
I used Sony Sound Forge, but almost every function should be available in your editing software.
I'm assuming some basic audio knowledge but I'll try to give enough info for an amateur to do it.
Lastly if *any* feature in your editing software has a live preview - USE IT. The result will be much faster and closer to what you want.
1. Record. See above.
2. De-esser. Reduces artifacts of sibilance. In SF it's under the Multi-Band Dynamics plugin included, some other programs you will need to get a plugin, there should be free ones on the net for more popular programs.
3. Adjust your volume. You want audible but not too loud, some of these processes amplify. You don't want to create clipping.
4. Sound Forge has a built-in feature called the "Wave Hammer" - it combines certain frequency boosts, bass boost (mild) and compression. In a way it's kind of like auto-tuning. If you don't have anything like this, it's not really essential, it just makes a poor mic sample sound better.
5. Flange - use a flange effect. I'm not quoting specific numbers because it will depend on what you started with to some extent, also start small and be prepared to apply a filter repeatedly, that actually helps create a more artificial, ethereal sound. I used a rate of 0.023 Hz and a depth of 76%, but I may do more than one pass and alter settings.
6. Pitch shift - Sovereign is not actually *that* low, but there is a bass boost that makes it seem so. Try dropping a few semitones to start. Live preview *really* helps here. You *might* want to do this after the Chorus effect. If there's an accuracy setting move it to low accuracy - again, sounds more synthetic.
7. Chorus. Start with 3 voices, attenuate high frequencies if possible (above 4k-5k), reduce the delay to something very short, say 30ms. If you add 3 more voices, invert the phase if you have the option to.
8. If you have a graphical EQ filter, esp. chart-based, drop out a narrow window of sound in the midbass range (160-600Hz) - you can move that range around a bit. I notice playing with the original Sovereign files there seemed to be a dip around there. Experiment to see if this makes your voice sound more Sovereigny.
9. Distortion - very important. SF has this chart-based again, very easy - you just adjust the output volume (original and modified) and then I grab the middle of the line and drop it 3-5 db, then repeat the process increasing that point to 3-5 db above baseline. The distortion makes the voice sound more artificial without being too obvious. I used a slew rate of 100 and a low-pass around 4500Hz.
10. Repeat as necessary - many of these steps will need to be done more than once to get where you want.
11. Almost forgot - time shift. I found that speaking slowly and deliberately is better for an even voice, and then I speed it up a few percent at the end and it seems to sound more mechanical.
And take notes! Makes it much easier the next time around.
Unfortunately I don't know how to automate this, and that would depend on the software you're using anyway.
Hopefully a few people will read this and we'll see a few more Sovereign improv videos on YouTube.
It would be an awfully complex but awesome real-time voice changer for a costume.